An alcoholic extract of Biophytum sensitivum was studied for its immunomodulatory and antitumor activity. The extract was 100% toxic at a concentration of 0.5 mg/ml to Dalton's lymphoma ascites (DLA) and Ehrlich ascites carcinoma (EAC) cells. B. sensitivum extract was also found to be cytotoxic towards L929 cells in culture at a concentration of 0.1 mg/ml. Administration of B. sensitivum extract (500 microg/dose/animal) could inhibit the solid tumor development in mice induced with DLA cells and increase the lifespan of mice bearing Ehrlich ascites carcinoma tumors by 93.3%. B. sensitivum treatment significantly (p<0.001) reduced the tumor cell glutathione (GSH) levels as well as serum gamma glutamyl transpeptidase (GGT) and nitric oxide (NO) levels in ascites tumor bearing animals. The total WBC count was also increased to 14,087 cells/mm(3) on the 12th day in BALB/c mice. The number of plaque forming cells also enhanced significantly (p<0.001), and bone marrow cellularity and beta-esterase positive cells were also increased by the administration of B. sensitivum extract.